1. Field of the Invention
The invention relates to a process for calculating the torque of a four-stroke internal combustion heat engine with electronically controlled injection, especially mounted in an automobile vehicle.
2. Discussion of the Background
More precisely, the measured torque is the mean gas torque produced by the firings of the air-gasoline mixture in the alp different cylinders. It is advantageous to measure the torque precisely over a large number of firings in order to optimize certain adjustments of the engine, in particular by virtue of the electronic injection computer, and in order to diagnose certain operating malfunctions, including misfires. A misfire in one cylinder of an engine with controlled injection may be due, for example, to lack of sparking, poor fuel supply or poor compression. Such recognition of poor firing is required by European regulations (European On Board Diagnostic: EOBD) or international regulations (On Board Diagnostic: OBD II), relating to diagnostic systems integrated into the vehicles in order to monitor exhaust system emissions for conformity with antipollution standards.
The process for measuring such a torque uses a device comprising an annular target, which is integral with the flywheel of the engine or with the crankshaft and which is provided on its circumference with marks such as teeth, which pass in front of a fixed sensor. The instantaneous value of the period of passage of the teeth in front of the sensor corresponds to the measurement of instantaneous power produced in each cylinder of the engine successively. Electronic computer means use the signal delivered by the sensor to calculate the mean gas torque Cg produced by each firing of the gaseous mixture in each cylinder of the engine.
In the particular case of a four-cylinder four-stroke gasoline engine operating in the Beau de Rochas cycle, each of the four strokes of the cyclexe2x80x94intake, compression, firing-expansion, exhaustxe2x80x94takes place during one particular half-revolution of the flywheel which is integral with the engine crankshaft. The kinetic energy acquired by the system in question, or in other words the crankshaft and flywheel with alternating masses, is the resultant of different instantaneous negative and positive torques exerted thereon during each of the different strokes of the engine""s operating cycle. The gas torque Cg is calculated in each half-revolution. This torque is generated during these phases of compression and firing-expansion of the gaseous mixtures confined respectively in two cylinders with contiguous firings (1 and 4, 2 and 3). The other two cylinders are then in intake and exhaust phases. Since the compression phases are less susceptible to variations or dispersion than the firing-expansion phases, it is considered that the gas torque Cg calculated over one half-revolution is relative to the firing cylinder, and therefore that it is an estimate of the mean gas torque over the two phases of compression and firing-expansion of the same cylinder, which therefore confines the same gaseous mixture.
As an example, the target is provided over its periphery with 57 regularly spaced, identical teeth, each formed by a peak and a hollow, and with one reference tooth, which has greater width equivalent to three other teeth and serves as the indexing origin to permit numbering of the said teeth. For a four-stroke four-cylinder engine, the angular period T of the firings concerns 30 teeth and is equal to half of the period of revolution of the crankshaft. For a four-stroke six-cylinder engine, the angular period of the firings T concerns only 20 teeth, and so on.
The fixed sensor may be of variable reluctance type, adapted to deliver an alternating signal of frequency proportional to the speed of passage of the teeth of the ring, or in other words proportional to the instantaneous speed of the flywheel.
A modern process for calculating the mean gas torque is described in French Patent Application filed under No. 95-06780 in the name of the Applicant, comprising:
producing a primary numerical value d, representative of the instantaneous duration of passage in front of the sensor of each tooth of the target,
from these numerical values dj, calculating a first secondary numerical value T representative of the total duration of passage in front of the sensor of each series of n teeth defining the angular interval of firings in the engine,
calculating a second secondary numerical value xcexa3 representative of the projection, on the phase reference line of the teeth corresponding to the origin of the angular periods of the firings, of the amplitude of the alternating component of the instantaneous durations dj of passage of the teeth in front of the sensor at the frequency of firings in the engine, this value xcexa3 being defined, for example, by the relationship:   Σ  =            ∑              j        =        0                    (                  n          -          1                )              ⁢          xe2x80x83        ⁢                  d        j            ⁢              cos        ⁡                  (                      2            ⁢            π            ⁢                          xe2x80x83                        ⁢                          j              /              n                                )                    
calculating the sought numerical value Cg from the following relationship (E):
Cg=xcex1(xcexa3/T3+xcex2/T2)xe2x80x83xe2x80x83(E)
which is valid over an interval T, regardless of engine rpm,
xcex1 and xcex2 being two experimentally determined constants.
The term xcex1 is a constant term proportional to the rotary inertia of the engine, and xcex2 is a term which is a function of the moment of intertia of the alternating masses. The irregularities of position of marks on the ring will, in a first approximation, perturb the value of the term xcex2/T2.
To ensure that measurement of the mean gas torque will be reliable and usable, especially in strategies for detection of poor firings of an engine, calculated by the injection computer, it is indispensable to eliminate defects of the target such as irregularities of position of the marks, which can cause unacceptable risks of false detection of poor firings, which risks increase with rpm.For this reason the objective of the invention is to acquire and correct defects of the target and to adapt to dispersions and to engine wear.
For this purpose, the object of the invention is a process for calculation of the torque of an internal combustion heat engine with injection controlled by an electronic computer, the engine being such that a target, for example in the form of a toothed ring provided with an indexing reference, is integral with the crankshaft and turns in front of a tooth-passage sensor, mounted in fixed position close to the target and delivering a signal to electronic torque-calculating means, said process comprising calculating, on the basis of numerical values dj represenative of the instantaneous duration of passage of each tooth in front of the sensor, a numerical value xcexa3 representative of the projection, on the phase reference line of the teeth corresponding to the origin of the angular periods of the firings, of the amplitude of the alternating component of the instantaneous durations dj at the frequency of firings in the engine, characterized in that it comprises correcting the defects of the target by the following stages:
distinguishing between the angular intervals Ti of the firings of the target relative to the reference, where i is an integer (equal to 1 or 2 for a four-cylinder engine);
assignment of a term xcex21 for each angular interval Ti;
recognition of torque conditions corresponding to nonfiring, such as cutoff of fuel injection into the cylinders;
acquisition of the term xcex2i under the said conditions of nonfiring by measurement of the engine torque Ci, which is proportional to the pressure Pmanifold in the intake manifold according to the relationship:
Ci=KPmanifold=xcex1(xcexa3N+xcex2i)N2
calculation of the engine torque Cgi delivered upon each firing, corresponding to each interval Ti of the target, from the term xcex2i, which is obtained from the equation:
Cgi=xcex1(xcexa3N+xcex2i)N2
where N is the engine rpm and K is a proportionality coefficient.